Heat-exchangers having a plurality of mutually parallel plates, with channels that are adapted to carry at least one heat transfer fluid, are well known in the art. Such parallel plate devices are often formed by folding a continuous sheet of metal to yield a so called “folded-fin” heat exchanger. The plates in such prior art heat-exchangers sometimes form a circuit path for circulation of two independent fluids, in counterflow, from one end of the heat-exchanger to the other. The plates are often connected to one another at their longitudinal edges by longitudinal braces or the like that are fixed together by a leak-tight wall extending over the entire length and height of the bundle of plates. The plates define a central zone for heat exchange between the fluids.
In some prior art heat exchange structures, the plates may have one or more corrugated sheets positioned between them, along the entire central heat transfer and exchange zone, to enhance heat exchange with the plates by increasing surface area and introducing turbulence in the flowing liquids. For example, U.S. Pat. No. 5,584,341, discloses a plate bundle for a heat-exchanger including a stack of mutually parallel metal heat-exchange plates. Each heat-exchange plate includes smooth-surfaced edges and a corrugated central portion which, with the associated heat-exchange plates, forms a double circuit for circulation of two independent fluids in counterflow. The plates are connected to one another at their longitudinal edges by connection structures, and have a zone of heat transfer and exchange between the fluids. Another zone is formed at the free ends of the plates for inlet and outlet of the fluids. The fluid inlet and outlet zones are formed by the plane ends of the heat-exchange plates.
A significant disadvantage in prior art heat-exchangers of this type is the inherent thermal impedance, i.e., resistance to thermal conduction through the thickness of the plate, associated with the materials used to form the heat-exchange plates. These prior art heat-exchange plates must have sufficient thickness so as to provide the requisite structural integrity needed for the physical demands that are placed upon such devices in normal use. Very often, the heat exchange plates are required to structurally support a portion of the heat exchanger. These design requirements typically require a minimum material thickness (e.g., a material thickness that is some minimum percentage of the plate's width or length) that results in a disadvantageously large inherent thermal impedance. Material selection is also dictated by this requirement, normally resulting in only metals being selected for the heat-exchange plates. Polymer materials typically exhibit significant dielectric and thermal insulating properties that preclude their use in heat-exchange plates, especially when they are required to provide structural integrity to the device.
U.S. Pat. No. 6,408,941, discloses a folded fin heat-exchanger that provides for the use of very thin materials and even polymeric materials such as one or more of the well known engineering polymers, e.g., polyhalo-olefins, polyamides, polyolefins, poly-styrenes, polyvinyls, poly-acrylates, polymethacrylates, polypropylene, polyesters, polystyrenes, polydienes, polyoxides, polyamides and polysulfides and their blends, co-polymers and substituted derivatives thereof, in its fabrication. However, there continues to be a need for enhanced air-to-air heat exchangers that are low cost and simple to manufacture.